Electronic balance with calibrating system

Abstract

In high-resolution electric balances a certain residual temperature coefficient remains even with a good correction of the temperature-dependent errors of the measured value sensor. The invention therefore is with respect to a balance with a built-in calibrating weight (standard) which responds with a new calibration switching in said calibrating weight if a given temperature changes has been exceeded since the last calibration. To this end, the balance comprises in microprocessor digital signal processing unit a separate memory area in which the output signal representing temperature value of a temperature sensor is stored during the calibrating process and also comprises a comparator which upon instruction compares the instantaneous output signal of the temperature sensor which the value stored in this separate memory area. If this difference exceeds a given amount, a signal element indicative of need to recalibrate using the calibrating weight is actuated. In addition, an elapsed time indicator can also be present which also actuates the signal element after the passage of a given time since the last calibration. In an advanced embodiment the apparatus will automatically cause recalibration to physically take place by having the signal processing unit control a motor which will switch the calibrating weight into weighing position. Said automatic recalibration taking place instead of or in addition to actuation of the signal element. Other physical science inputs can also be sensed and utilized by themselves or in combination in determining when recalibration should occur.

What is claimed is: 
     
       1. An electronic balance scale having a built-in calibrating system comprising: a weight-measured value sensor,   a temperature sensor having a real time digital output,   a built-in calibrating weight, said weight being operably moved into a sole-weight-to-be-measured position upon an initiation of a calibration event,   a microprocessor/digital signal processing unit,   said unit comprising: a mathematical computation unit,   a memory unit having a plurality of memory areas for storing at least magnitudes, including a first, second, third, a preset-difference memory area, and at least one other memory area,   a comparator unit to compare the magnitude of a first memory area compared to that of a second memory area and indicate in a third memory area which magnitude of said first and second memory areas is larger and by what magnitude of difference,     a memory with a built-in program of instructions,   a calibration factor stored in one of said other memory areas,   said factor computed at an initiation of a calibration event utilizing only said built-in calibrating weight,   said digital output of said temperature sensor being inputted into said second memory area, said first memory area storing the temperature digital output of said temperature sensor at the occurrence of the last calibration event,   a display and operating panel having an actuatable signal element,   said signal processing unit under control of said program continuously reading said temperature sensor, and by said comparator unit comparing a temperature at said sensor as stored at said second memory area with a temperature as stored at said first memory area and if said difference is greater than a number stored at said preset difference memory area then said signal element is actuated indicating that a new calibration event utilizing only said built-in calibrating weight should be initiated.   
     
     
       2. Electric balance according to claim 1, wherein the signal element is a light-emitting diode. 
     
     
       3. Electric balance according to claim 1, with an LCD display field, wherein the signal element is a symbol in a display field of said display and operating panel. 
     
     
       4. Electric balance according to claim 1, with a fluorescent display field, wherein the signal element is a symbol in a display field of said display and operating panel. 
     
     
       5. Electric balance according to claim 4, wherein the symbol resembles a weight piece. 
     
     
       6. Electric balance according to claim 5, wherein the signal element blinks when actuated. 
     
     
       7. Electric balance according to claim 1 including a preset elapsed time memory wherein an elapsed time indicator is additionally present in the digital signal processing unit, which indicator is reset to zero at every calibrating event. 
     
     
       8. Electric balance according to claim 1 including a preset elapsed time memory wherein an elapsed time indicator is additionally present in the digital signal processing unit, said indicator being read by said instructions, said instructions resetting said indicator to zero upon some predetermined value, as determined by at least said preset elapsed time memry, in said indicator being reached, and said reset event indicating a calibrating event. 
     
     
       9. Electric balance according to claim 8, wherein said digital signal processing unit likewise actuates the signal element upon said reset event. 
     
     
       10. Electric balance according to claim 8, wherein as the reading of the elapsed time indicator increases, the given amount by which the instantaneous output signal of the temperature sensor as stored in said second memory area must differ from the value in said first memory area in order to initiate the actuation of said signal element is decreased. 
     
     
       11. Electric balance according to claim 10, wherein the microprocessor/digital signal processing unit actuates both the signal element and a motor of the calibrating system which operably moves said built-in calibrating weight into sole-weight-to-be-measured position. 
     
     
       12. Electric balance according to claim 1, wherein the microprocessor/digital signal processing unit actuates both the signal element and a motor of the calibrating system which operably moves said built-in calibrating weight into sole-weight-to-be-measured position.